Internal Combustion Using a Steam-Cycle Coke Engine?

It's an interesting notion (recovering high temperature waste heat from an IC engine to drive a pyrolytic conversion process) . Would a practical application be based on stationary engines? This would allow controlled, continuous feed of solid organic by products to the pyrolysis unit, separation of liquid products (which have more value as chemical feedstocks than as IC fuel) from the exhaust and return of the combustible exhaust gases to the IC engine.

Yes, a timber-fed chemical 'factory' tied in with, say, electricity generation would seem a possible way to go. Then the issue more about whether the feedstocks generated are valuable enough to make it add up.

You might be able to make a bit of steam from your waste heat. But it there is no way it will contain enough energy to gasify the biomass.

It is entirely possible to run a IC engine on wood. But a conventional gasifier is a much simpler way to do it.

These folk drove right around Australia in the late 1980s using wood fuel that they harvested from the roadside.

http://www.angelfire.com/ak5/energy21/woodfire.htm

Am I right in thinking there would be enough (waste) energy to at least react some of the fuel necessary. It the further component was natural gas, etc then the exhaust should still be a 'clean' stream of H20 & CO2. And could be reused with little extra top up water.

I agree that a stationary application is going to present many fewer problems, but I do like the idea of driving around with a tank of carbon dust!

The key issue, if the process is at all workable, is how much non 'coke' fuel would be needed to make the process sustainable. If the ratio is anything over 2:1 [C to CH4] then it likely can't fly. The added complication is not worth the efficiency I'd imagine; I would like to get some back-of-the-envelope figures on this though...

I have read a bit on wood-gas & it was an aspect of coming up with this idea. The concept of running around with a wood-burning stove on the back bumper is perhaps the crudest way of getting 'free' gas to an engine. I suppose my process is an attempt to reuse waste heat (that straight wood gasifiers can also do) but with a more compact and efficient 'on-board' tank of fuel.

Back of the envelope calculation?

I just did one, but I picked up a mistake after I posted it. I'll have another go later.

Ok, here we go. I will put up this calculation, which glosses over all sorts of practical problems and may even contain some basic errors. But we have to make a start somewhere, don't we? I would be happy for people to object, modify, recalculate as they see fit.

Let's just do a simple calculation to scope things out, assuming we get 100% efficiencies in all our processes.

Imagine that we burn 1 kg of petrol. That contains 45 MJ of energy.
Let's say that 30% of the energy goes out with the exhaust. That is 15 MJ.
Now, imagining that we have a 100% efficient steam superheater that recovers ALL of that energy, How much carbon can we gasify?
Heat of gasification is 9.75 MJ/kg of Carbon
So, we can gasify 1.384 kg of carbon, neglecting kinetics and temperature.

How much gas will that generate?
Carbon monoxide 3.23 kg
Hydrogen 0.23 kg
Total mass of gas is 3.46 kg

What is the heat of combustion of those gases?
Carbon monoxide (10 MJ/kg) gives 32.41 MJ
Hydrogen (141 MJ/kg) gives 32.53 MJ
Total heat of combustion is 64.95 MJ

Of course, that is a perfectly efficient process, but it is better than I would have thought!

Morrie, thanks so much for investing the time in getting those figures out.

I have to say I am (also) liking the way those results sound!

I'm sure it's clear that I'm not a whizz with calculating chemical processes, but if there is any huge holes in what you've come up with I can't spot them.

I have just read: "Catalytic steam methanation of coal is an almost thermoneutral process - 2C + 2H2O --> CO + H2 ΔH = 8kJ/mol" (www.anl.gov/PCS/acsfuel/preprint archive/Files/41_1_NEW ORLEANS_03-96_0216.pdf). Although I was never very good at understanding mols at school I would hazard a guess that this means the process is not going to be so draining of heat that it would not self-sustain at a relatively constant engine load.

It did also occur to me that a little more SH steam could be added by the cooling system (especially if spray cooling was utilised [a previous idea I submitted - http://cr4.globalspec.com/thread/46514]). Since a further quarter or so of the thermal energy disappears into block cooling I would have thought a combined steam generator could make further syngas possible.

I doubt the system would get all that close to 100% efficient, but in mid-range operation of the engine I would like to believe the system could halve the amount of petrol (replaced with charcoal) for such a design.

That's: 65MJ * (2/3+1/4) = 111.5MJ for combined heat recovery. Necessary efficiency 45MJ (petrol)/111.5(C) = 39%

Of course I don't know how much weight/bulk the process would add to the engine, but it still seems worth further discussion...

Cheers!

>>>I have just read: "Catalytic steam methanation of coal is an almost thermoneutral process - 2C + 2H2O --> CO + H2 ΔH = 8kJ/mol"

I think, if you look closely, you will find that the equation you are referring to is

2C+2H2O --> CO2 + CH4

Thats quite a different scenario from making synthesis gas, but interesting that it is close to thermoneutral, just the same.

Woops. Should read more carefully!

That should be:

C (s) + H2O (g) --> CO (g) + H2 (g) ΔH deg = +131.3 kJ
CO (g) + H2O (g) --> CO2 (g) + H2 (g) ΔH deg = -41.2 kJ
C (s) + 2H2O (g) --> CO2 (g) + 2H2 (g) ΔH deg = -82.4 kJ

which is somewhat different.